This invention relates to refractory fibers of a type suitable for composite reinforcement. More particularly, this invention relates to refractory fibers formed by chemical vapor deposition of an inorganic sheath onto a carbon filament, which fibers preferably have a diameter less than 10 microns.
Reinforced composites may be formed of refractory fibers dispersed in a matrix that may be metal, plastic or ceramic. For example, an aluminum composite may be reinforced by boron fibers. Suitable boron fibers are produced by depositing boron onto a core such as carbon fiber or tungsten wire. Heretofore, the boron fibers typically have diameters greater than 100 microns. Such diameters are necessitated in part because of the thickness of the core, which is typically greater than 10 microns in diameter. In general, increasing fiber diameter reduces tensile strength. Also, manipulation of thick fibers, for example, for packing a mold, is rendered more difficult as a result of increased resistance to bending. Furthermore, the critical stress transfer length increases with diameter, so that thicker fibers require longer lengths for comparable reinforcement.
It is an object of this invention to provide a thin refractory fiber having a diameter less than 100 microns and preferably less than 10 microns, which fiber is formed by chemical vapor deposition of an inorganic sheath onto a microscopic carbon filament. Such thin refractory fibers exhibit increased tensile strength, facilitate processing and improve composite properties.